Igneous Rock Notes

Igneous rock forms when magma cools and solidifies.

Composition Texture Classification Felisc or Mafic Intrusive or Extrusive

Classification Felsic – light colored, less dense Granite Felsic – light colored, less dense Rich in aluminum, potassium, silicon, and sodium. Rhyolite

Classification Mafic – dark colored, more dense Gabbro Mafic – dark colored, more dense Rich in calcium, iron, and magnesium Basalt

Texture Intrusive Igenous Rock – inside Earth’s crust (corase-grained)

Texture Intrusive Igneous Rock Formations Pluton: Large, irregular shaped intrusive bodies Batholiths: The largest of all igneous intrusions Stocks: Intrusive bodies that are exposed over smaller areas than batholiths Dikes: Sheetlike intrusions that cut across previous rock units Laccolith: Sheetlike intrusions that are oriented parallel to previous rock units Volcanic neck: A column of igneous rock formed when magma hardens with in a vent

Texture Extrusive Igenous Rock – on Earth’s surface (fine-grained)

Texture Extrusive Igneous Rock Formations Lava Flow: Formed when lava erupts from a volcano Fissure: Long cracks in Earth’s crust where lava can flow

Igneous Rock Flow Chart rock melts rock cools igneous rock Slow cooling (coarse-grained) pressure composition temperature Fast cooling (fine-grained)